1. Field of the Invention
The present invention relates generally to devices and methods for the non-destructive inspection of structural systems. The present invention relates more specifically to devices and methods for the inspection of aircraft structural systems, particularly those associated with the attachment of a wing structure to an aircraft fuselage.
2. Description of the Related Art
Many of today's aircraft, including military aircraft, are being utilized past their original designed lifetime. This utilization creates inherent problems related to the structural limitations brought about because of the age of the aircraft. Repairs and structural modifications can extend the life of the aircraft but in the process can position structural components that affect the ability of existing test systems to perform nondestructive inspection (NDI) on areas where these modifications have been made.
An example of the above described concern is in the area of wing attachment fittings that serve to connect the wing structure to the aircraft fuselage. If a defect such as a crack is identified in an attachment fitting, the repair protocol calls for drilling or reaming out the fastener hole in the attachment fitting “stack-up area” (described in more detail below) and bushing the hole to allow for the original size fastener to be reinstalled. This procedure, however, presents an inspection problem, generally requiring the removal of the wing to gain access to the areas of interest. The process of wing removal and reinstallation is costly and not always practical given the location of the aircraft and the availability of equipment and trained personnel.
A method and a system to inspect the fastener hole of an attachment fitting stack-up without wing removal are therefore needed. Conventional NDI methods and systems are not capable of inspecting through a bushed hole with the kind of sensitivity-to-defect that is required to identify and locate flaws and defects of the size that must be identified (or confirmed absent) in order to keep the aircraft in service.
The present invention addresses the above described issues through the use of not only an inspection procedure and an inspection probe structure, but also a specific application of each. This specific application may generally be referred to as a 2nd layer bushing inspection of an aircraft wing attachment fitting using ECP (electric current perturbation) sensing.